1. Field of the Invention
This invention relates to communication systems. In particular, the invention relates to determining and displaying the service level of a digital television broadcast signal.
2. Description of Related Art
Digital Television (“DTV”) is a broadcast technology that will transform television, as we now know it. Particularly, DTV is a new “over-the-air” digital television system that will be used by the nearly 1600 local broadcast television stations in the United States. The DTV standard is based on the Advanced Television System Committee (ATSC) Digital Television Standard A/53 (ATSC Doc. A/53, Sep. 6, 1995). With DTV, television pictures, sound, and new data services will be transmitted digitally, rather than as an analog signal. The increased capabilities and new services of DTV are made possible through the use of digital compression techniques that allow more information to be transmitted in the same amount of spectrum used by an existing television channel. The data rate of the DTV signal within the standard 6 MHz broadcast television channel is 19.44 Mbps. This allows for the transmission of programs with very high resolution and sound quality, much better than currently available analog broadcast technology, allowing for movie-quality picture and CD-quality sound and a variety of other enhancements. For example, DTV permits transmission of television programming in new wide screen, high resolution formats known as high definition television (HDTV). In addition, the new DTV television system allows transmissions in standard definition television (SDTV) formats that provide picture resolution similar to existing television service. Not only will broadcasters be able to broadcast at least one high definition HDTV program, they may also simultaneously transmit SDTV programs using a single television channel.
The DTV system also makes possible the delivery of digital data services to a television and/or computer alone, or simultaneously with, television and audio programming. Of particular interest, beyond the transmission of audio/visual (A/V) information (i.e. the television program), is that these digital broadcast signals from the television networks include additional data that may carry any number of valuable assets. Particularly, the data portion of the digital broadcast signal may carry Advanced Television Enhancement Forum (ATVEF) content (e.g. graphics, video, text, audio, and other types of data) and Streaming Internet Protocol (IP) data (e.g. graphics, video, text, audio, and other types of data). Using this data transmission capability, it will be possible for broadcast stations to send additional data content such as publications (e.g. a local “electronic newspaper”), news, music, program schedules, computer software, or virtually any other type of information/data, at the same time that they transmit regular television programming or in lieu of television programming.
For example, a television network may transmit a financial news show (i.e. the A/V information from the digital broadcast signal) with an announcer talking about what happened to the stock market during the day, simultaneously, the broadcast station can transmit digital data (e.g. graphics, video, text, audio, and other types of data), such as streaming stock quotes, information about a company—e.g. a news story or a picture of the company headquarters, graphs, cartoons, or virtually any type of information, for example, in a window under the announcer. The DTV system also provides the flexibility to support the introduction of new services in the future, as technology and viewer interests continue to develop.
For the compression of video signals, the ATSC DTV Standard requires conformance with the main profile syntax of the Moving Pictures Experts Group (MPEG)-2 video standard. Employing this standard, the amount of data needed to represent television pictures is reduced using a variety of tools, including a motion compensated discrete cosine transform (DCT) algorithm and bi-directional-frame (B-frame) prediction. For the compression of audio signals, conformance with the ATSC DTV Standard A/52 (ATSC Doc.A/52, Dec. 20, 1995) is required, which specifies the Digital Audio Compression (AC-3) Standard. The AC-3 perceptual coding system, which was developed by Dolby Labs, can encode a complete main audio service which includes left, center, right, left surround, right surround, and low frequency enhancement channels into a bit stream at a rate of 384 kilobits per second (kbps).
The service multiplex and transport layer of the ATSC DTV Standard is a compatible subset of the MPEG-2 systems standard that describes a means of delivering a digital data stream in fixed-length “packets” of information. Each packet contains only one type of data: video, audio or ancillary (e.g. data). There is no fixed mix of packet types, which further helps provide flexibility. Channel capacity can be dynamically allocated in the transport layer, under the direct control of the broadcaster. The ATSC DTV Standard has been optimized for terrestrial digital television delivery, where channel bandwidth is limited and transmission errors and data loss are likely. Within the transport layer, the packets of video, audio, closed captioning and any other data associated with a single digital television program are combined using a mechanism to ensure that the sound, pictures and closed captioning information can be synchronized at the receiver. Data describing multiple television programs (e.g. program guide information), or unrelated data for other purposes, are also combined in the transport layer.
A problem with Digital Television (DTV) is that present methods to accurately tune a digital receiver, by determining the best position of the antenna (indoor or outdoor), to receive the “best service level” of a DTV broadcast signal are inadequate. The “best service level” corresponds to the digital receiver receiving the greatest amount of the actual data packets (video, audio, or data) contained within the digital broadcast signal, as possible.
For example, a user can attempt to utilize a video component of the digital broadcast signal to determine the “best service level”, but this is very imprecise. Under this scenario, a user when trying to find the best reception for a certain channel, will tune to a channel and adjust their antenna (indoor or outdoor) until what they believe is the “best” video is displayed. The user may adjust their antenna in one direction and find that the video becomes blocky or chunky (indicating missing data packets) and then turn the antenna in the other direction and the video appears to more complete. However, there is no way for the user to be objectively sure that they are indeed getting the “best service level” (i.e. that the greatest amount of data packets of the digital broadcast signal are actually being received) for the best video picture possible. A user could try to tune an antenna based purely on an audio component but this is even more complicated and problematic than the video case.
Moreover, if a viewer wants to obtain a pure data broadcast that has no visual or audio component to use for adjusting their antenna, it is virtually impossible for the user to determine the “best service level”, or any sort of service level, to ensure that they are actually receiving the data packets of the digital broadcast signal. Unfortunately, presently, users do not have adequate ways to be objectively sure that they are indeed getting the “best service level” such that they are receiving the greatest amount of data packets of the digital broadcast signal as possible.
Some solutions to determine the degree of service level have been previously utilized with satellite broadcasts. These solutions include using “Signal Strength” and Signal/Noise (Carrier/Noise) ratios. For example, most satellite receivers use “Signal Strength” to identify the best antenna position. However, just because the best signal is found, this does not necessarily mean that the “best service level” has been found. Particularly, although these two solutions may provide an adequate indicator of service level, these solutions are problematic in that neither multi-path interference or other interference patterns can be detected utilizing these solutions. For example, many multi-path interference issues arise with satellite transmissions that utilize 8 VSB (vestigial sideband) and COFDM (Coded Orthogonal Frequency Division Multiplexing) standards. Moreover, these two solutions are only indicators of what the actual data packet error rate (i.e. the data packet loss over time) is. They only measure signal strength and not true transport quality. Accordingly, they do not directly measure the actual data packet error rate and thus the “true” service level.